Class: Cbc::ConflictSolver

Inherits:
Object
  • Object
show all
Defined in:
lib/ruby-cbc/conflict_solver.rb

Instance Method Summary collapse

Constructor Details

#initialize(problem) ⇒ ConflictSolver

Returns a new instance of ConflictSolver.



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# File 'lib/ruby-cbc/conflict_solver.rb', line 5

def initialize(problem)
  # clone the model minus the objective
  @model = Model.new
  @model.vars = problem.model.vars
  @model.constraints = problem.model.constraints
  @problem = problem
end

Instance Method Details

#find_conflict ⇒ Object 



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# File 'lib/ruby-cbc/conflict_solver.rb', line 13

def find_conflict
  crs = Util::CompressedRowStorage.from_model(@model)
  continuous = is_continuous_conflict?(crs)
  unless continuous
    p = Problem.from_compressed_row_storage(crs, continuous: false)
    return [] unless infeasible?(p)
  end
  clusters = [crs.nb_constraints]
  max_iter = 1
  conflict_set_size = 0
  loop do
    range_idxs = first_failing(conflict_set_size, crs, continuous: continuous, max_iterations: max_iter)
    break if range_idxs.nil?
    puts "RANGE #{range_idxs}"
    crs = crs.restrict_to_n_constraints(range_idxs.max + 1)
    crs.move_constraint_to_start(range_idxs)
    clusters.insert(0, range_idxs.size)
    clusters[-1] = range_idxs.min - conflict_set_size
    conflict_set_size += range_idxs.size

    # Test conflict set
    crs2 = crs.restrict_to_n_constraints(conflict_set_size)
    problem = Problem.from_compressed_row_storage(crs2, continuous: continuous)
    if infeasible?(problem)
      puts "CONFLICT"
      clusters.delete_at(-1)
      break if clusters.size == conflict_set_size

      crs = crs2
    end

    nb_clusters_one_constraint = 0
    clusters.reverse_each do |nb_constraints|
      break if nb_constraints > 1
      nb_clusters_one_constraint += 1
    end
    if nb_clusters_one_constraint > 0
      crs.move_constraint_to_start((crs.nb_constraints - nb_clusters_one_constraint)..(crs.nb_constraints - 1))
      clusters[nb_clusters_one_constraint, clusters.size - nb_clusters_one_constraint] =
        clusters[0, clusters.size - nb_clusters_one_constraint]
      clusters[0, nb_clusters_one_constraint] = Array.new(nb_clusters_one_constraint, 1)
    end

    conflict_set_size = crs.nb_constraints - clusters[-1]
    puts "CLUSTERS #{clusters.inspect}"
    puts "VARS #{crs.col_idx.uniq.size}"
  end
  crs.model.constraints[0, conflict_set_size]
end

#is_continuous_conflict?(crs) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/ruby-cbc/conflict_solver.rb', line 63

def is_continuous_conflict?(crs)
  problem = Problem.from_compressed_row_storage(crs, continuous: true)
  infeasible?(problem)
end